Wednesday, May 1, 2013

New paper finds 'no consensus on the sign' of cloud effects on climate

A paper published today in the Journal of Climate finds "climate models have no consensus on the sign of the longwave cloud feedback." Translation: we don't know if it is positive or negative, whether radiative 'greenhouse' effects from clouds are positive or negative. Longwave infrared feedback from water vapor/clouds is essential to determine whether the miniscule radiative effect from CO2 is amplified ['positive feedback' as claimed by the IPCC] or dampened ['negative feedback' as shown by many skeptics] due to changes in water vapor. Further, the paper states "stratospheric water vapor and temperature changes may both act as a positive feedback mechanism during global warming," but satellite observations show stratospheric water vapor as well as total column water vapor are declining in defiance of the IPCC computer models.

Observations of stratospheric water vapor from Soloman 2010: Black line is from radiosonde observations collected in only one location {Boulder CO}. Global satellite data is shown by the diamonds starting in 1993 and indicate a declining trend since ~1993.

This paper mainly addresses two issues that concern the longwave climate feedbacks. First, it is recognized that the radiative forcing of greenhouse gases, as measured by their impact on the outgoing longwave radiation (OLR), may vary across different climate models even when the concentrations of these gases are identically prescribed. This forcing variation contributes to the discrepancy in these models’ projections of surface warming. A method is proposed to account for this effect in diagnosing the sensitivity and feedbacks in the models. Second, it is shown that the stratosphere is an important factor that affects the OLR in transient climate change. Stratospheric water vapor and temperature changes may both act as a positive feedback mechanism during global warming and can not be fully accounted as a “stratospheric adjustment” of radiative forcing. Neglecting these two issues may cause a bias in the longwave cloud feedback diagnosed as a residual term in the decomposition of OLR variations. The climate models have no consensus on the sign of the longwave cloud feedback after accounting for both issues.Prior posts on the multiple failures of computer modelling of clouds